In situ production of hydrocarbon values from oil shale using H{HD 2{B S and CO{HD 2{B

ABSTRACT

Kerogen is recovered from oil shale deposits by introducing CO2 and H2S in water into the deposits under pressure and then shutting in the deposits to allow the H2S and CO2 solutions to dissolve the inorganic matrix material in the deposits. Kerogen is then recovered from the deposits, preferably as a colloidal suspension.

l6-3O7 l 0 2 SE 399159.234 United States Patent 11 1 1111 3,

Pelofsky Oct. 28, 1975 [54] IN SITU PRODUCTION OF HYDROCARBON. 3,322,1945/1967 Strubhar 166/307 V LUE FROM 01 SHALE USING 5 AND 3,484,36412/1969 Hemminger 208/1 1 CO 3,565,784 2/1971 Schlinger et a1. 208/1] 23,605,889 9/1971 Closmann et al, 166/307 [75] Inventor: Arnold H.Pelofsky, East Brunswick, 3,617,472 1 H1971 Schlinger et a1 208/11 N3,700,280 10/1972 Papadopoulos et al. 166/271 0 3,739,851 6/1973 Beard166/254 Asslgneel Clues Service Research & 3,741,306 6/1973 Papadopouloset a1 166/271 Development Company, Cranbury, 3,753,594 8/1973 Beard166/271 NJ. 3,804,169 4/1974 Closmann 166/272 3,804,172 4/1974 Closmannet a]. 166/272 [22] Filed: Aug. 28, 1974 [21] Appl. No.: 501,310 PrimaryExaminer-Henry C. Sutherland Assistant Examiner-Jack E. Ebel Attorney,Agent, or Firm-George L. Rushton [52] US. Cl 166/307; 299/5 [51] Int.Cl. E21B 43/16; E21B 43/25 [58] Field of Search 166/271, 305 R, 307;[57] ABSTRACT 208/11; 252/855 (3; 299/5 Kerogen is recovered from oilshale deposits by introducing CO and H 8 in water into the depositsunder [56] References C'ted pressure and then shutting in the depositsto allow the UNITED STATES PATENTS H S and CO solutions to dissolve theinorganic matrix 3,074,877 1 /l963 Friedman 208/11 material in thedeposits Kerogen is then recovered 3,122,493 2/1964 Thomsen 208/11 fromthe deposits, preferably as a colloidal suspension. 3,265,608 8/1966Crawford 1 208/11 3,278,233 10/1966 Hurd et a1 299/4 7 Claims, 2 DrawingFigures US. Patent Oct. 28, 1975 3,915,234

22 FIG.

IN SITU PRODUCTION OF HYDROCARBON VALUES FROM OIL SHALE USING H S AND COBACKGROUND OF THE INVENTION This invention relates to the recovery ofhydrocarbon substance, largely insoluble in benzene, and which isdispersed throughout an inorganic matrix composed principally ofcarbonates along with other minor constituents. The kerogen in oil shaleis relatively rich in hydrogen and will yield a benzene-soluble material(bitumen) on heating.

Many proposals have been made for recovering usable hydrocarbons fromoil shales, most of which involve the use of heat in one form or anotherto soften or liquefy the kerogen for conversion to bitumen or forfurther conversion to produce both liquid and gaseous products. The heatmay be applied in situ, or the shale may be mined by conventional miningmethods, with subsequent heating or retorting of the mined shale. Inconventional in situ retorting, a heating agent is injected into one ormore wells extending into the shale deposit, and product is producedthrough the same or separate wells. It is also known to inject air intothe formation to ignite the kerogen and form a combustion front which isthen moved through the formation in a conventional manner to liquefy andpartially gasify the kerogen and carry the liquid and gaseous productsthrough the formation to wells from which it may be recovered. In situprocesses frequently involve fracturing the shale deposit to facilitatecontact between heating agents and kerogen.

It has also been suggested that kerogen can be recovered from shaledeposits by dissolving the inorganic matrix, either by the use ofsolvents such as water or acidified water or by introduction ofmicroorganisms. Such processes have not, however, proven satisfactoryand generally must rely on fracturing or otherwise breaking up thedeposits to allow contact with the solvent or microorganisms over asufficiently large area.

It is an object of the present invention to recover kerogen from shaledeposits by means of a novel in situ recovery process.

SUMMARY OF THE INVENTION Hydrocarbon values are recovered from asubterranean deposit of oil shale by introducing a mixture of H 5 and COin water under pressure into the deposit. This is preferablyaccomplished by introducing water, CO and H 8 into the deposit throughwells extending into the deposit. Introduction of water, CO and H 5 iscontinued until the pressure in the deposit at the point of introductionis increased to between about 200 and about 1000 psi above the formationpressure of the deposit. The deposit is then shut in until the pressuredrops to less than about 50 psi above formation pressure, at which timehydrocarbon values, usually in the form of kerogen, may berecovered'from the deposit. In a preferred embodiment, the sequence ofinjection of H 8, CO and water under pressure, followed by shutting inuntil pressure drops, is continued until the acids have penetrated thedeposit throughout spheres of a radius between about 50 and about 500feet about the points of introduction. It is also preferred inpracticing the invention that the CO and H 5 dissolved in water beintroduced into the deposit as a saturated aqueous solution, betweenabout 30 and about volume percent of which comprises a saturatedsolution of CO with the remainder being a saturated aqueous solution ofH 5.

BRIEF DESCRIPTION OF DRAWING FIG. 1 is vertical, cross-sectional viewillustrating use of the present invention in recovery of hydrocarbonvalues from an oil shale deposit.

FIG. 2 is a horizontal, cross-sectional view further illustrating use ofthe invention in recovering hydrocarbon values from oil shale deposits.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides animproved method for recovering hydrocarbon values from shale deposits byat least partially dissolving the inorganic matrix of the deposits,thereby substantially increasing the permeability of the deposit. Thekerogen in the deposits may then be recovered by suitable means such asin the form of a colloidal suspension or may be further converted insitu as by the use of heat, microorganisms, etc. in a conventionalmatter for recovery of hydrocarbon values in the form of bitumen. It isthe purpose of the present invention to increase permeability of theshale deposits to the point where conventional methods such as thosementioned above for recovery of hydrocarbon values from the deposit maybe employed.

In the chemical art, it is well recognized that CO dissolved in waterforms a weak acid written as H CO Similarly, H 5 can be dissolved inwater. And it is further recognized that both of these solutions aredilute, in that the amount of gas dissolved in a unit of water issomewhat low, e.g., about 28.2 g. of CO dissolve in 1 liter of water at100 C and atm. Thus, although saturated solutions of CO and H 5 in waterare described, it is customary to physically entrap additional gas, bypressure, in the solvent water, thereby having a reserve of gasavailable to ensure saturation of the solution. The combination of gasesdissolved in water can be simply expressed as H 8 and CO in water."

While any convenient method may be used for contacting H 5 and CO withthe inorganic matrix of the shale deposit, it is preferred that anaqueous medium saturated with H 8 and CO be used. The H 8 and CO may beadded to the water at the surface or more preferably at or near thebottom of the wells extending into the shale deposit. Saturated aqueoussolutions of CO and H 8 are preferred. Greater solubility is obtainedusing water not contaminated with inorganic material but for practicalreasons of availability and cost, brine such as connate water obtainedfrom the shale deposit or surrounding formations is frequently apreferred medium. Use of such solutions increases the time required fordissolving inorganic matrix material because of the lower solubility ofthe gases in the brine as opposed to fresh water. While the desiredacids can, of course, be formed by adding CO and H 8 either at thesurface or at the bottom of the wells, it will generally be found to becheaper and therefore more desirable to pump the gas and waterseparately and add the gas to the water at the bottom of the injectionwells.

For convenience, the term H SH O" will be used in this disclosure torepresent the phrase, H S dissolved in water.

The inorganic matrix of typical shale deposits comprises about 95percent quartz, feldspars, dolomite and calcite with the remaining 5percent including illite clay materials, pyrite and analcite. Theparticular combination of acids used in practicing this invention, i.e.,H SH O and H CO formed by saturating water with H 8 and CO is especiallybeneficial because certain of the components of the inorganic matrix arereadily dissolved by the H CO while some other components are usuallydissolved by the H SH O. This combination of acids also gives betterresults than other possible solvents, such as sulfuric or nitric acid,and leads to fewer environmental problems in the event of seepage out ofthe deposit into the surrounding water sheds or formations. While anespecially preferred mixture of acids for use in practicing thisinvention comprises about 50 percent by volume of water saturated with H8 and 50 percent by volume of water saturated with CO ranges betweenabout and about 70 percent for either the H S- or the CO -saturatedwater are completely acceptable. An excess of gas is normally used insaturating the water to insure maximum concentration of acid. The wateritself can, as mentioned above, be fresh water or brine. Connate water,recycled water, etc., may, of course, be used. Gases may be added to thewater in the wells by aspiration or other suitable techniques and thedegree of saturation can readily be checked by measuring the pH of theresulting solution. An increase of 2 pH units from the maximum acidityobtainable generally indicates the need for addition of increasedquantities of gas.

In practicing the invention, H S-H O and H CO formed as described aboveby introduction of H S and CO into water being injected into the depositthrough wells, may be forced into the deposit under pressure until thepressure at the bottom of the wells is raised to between about 200 andabout 1000 psi above the formation pressure of the deposit. The wellsare then shut in to allow time for the acid mixture to dissolve theinorganic matrix. As dissolution occurs, the acid spreads through thedeposit and pressure gradually drops. When pressure has dropped to lessthan 50 psi above formation pressure of the deposit, hydrocarbon valuesmay be recovered from the deposit, although it is preferred that thesteps of injecting water saturated with CO and H 8 and then shutting inthe wells to allow pressure to again drop to near formation pressure becontinued until the H2sH2O and H CO have penetrated the formation (bydissolving the inorganic matrix) throughout spheres of a radius ofbetween about 50 and 500 feet from the bottom of each injection well. Toavoid loss of kerogen to surrounding formations, it is preferred thatthe peripheries of these spheres remain at least 50 feet from theboundaries of the shale deposit.

Once the permeability of the formation has been sufficiently increasedby dissolving inorganic matrix as described above, kerogen may berecovered directly from the deposit or may be converted into bitumen forrecovery of hydrocarbon values from the deposit in a conventionalmanner. A preferred method of recovering hydrocarbon values involves therecovery of kerogen in the form of a colloidal suspension in water andfor this purpose suitable surfactants such as benzene sulfonic acid,naphthenic acid or isostearic acid may be added in suitable amounts suchas 0.1 to 1 volume percent to facilitate formation of free flowingsuspensions. Such suspensions may frequently contain between about 10and about 30 weight percent kerogen. Alternatively, other means ofrecovering hydrocarbon values, such as heating the kerogen or addingmicroorganisms to the injected water to transform kerogen to bitumen,may be employed. It should be understood that in producing eithercolloidal suspensions of kerogen or in producing bitumen from the shaledeposit following treatment in accordance with the invention, primary,secondary and even tertiary production techniques may be used.

In practicing the invention, it will generally be found that, followingraising of the pressure at the bottom of the wells to between about 200and 1000 psi above formation pressure, a period of at least about 2weeks will be required for the pressure to drop to within about 50 psiof formation pressure and that a total time of between 1 month and about1 year is frequently required to obtain the desired penetration of theshale deposit throughout the spherical volumes referred to above. Whilekerogen or hydrocarbon values in other forms may be recovered at the endof each of the above described pressure cycles, it is preferred thatsuch withdrawal not be attempted until the degree of penetrationdescribed above has been obtained since efficiency is thereby increased.

In practicing the invention, it is important to avoid fracturing theshale deposit since fractures formed be yond the area of deposit fromwhich it is desired to withdraw hydrocarbon values may result inexcessive loss of bitumen into other areas of the deposit in instanceswhere kerogen is transformed to bitumen and in any event fracturesextending to the boundaries of the deposit will result in excessive lossof kerogen or bitumen to permeable surrounding or underlying forma tionsor overburden. For this reason, it is preferred that the invention bepracticed in shale deposits having a thickness of at least about 200feet and that the periphery of each of the spheres of effected area inwhich the inorganic matrix is dissolved by the H CO and H SH O remain aminimum of at least about 50 feet from the boundary of the deposit.Overlapping of such affected spheres is of course permissible andfrequently desirable to insure maximum recovery of hydrocarbon values,but it is preferred that overlapping be kept to the minimum necessary toobtain desired recovery of hydrocarbon values.

While this invention may be operated at elevated temperatures ifdesired, such operation usually leads to excessive loss of heat and itis therefore preferred that the invention be practiced at ambientformation temperature. Furthermore, the solubility of H 8 and COdecreases with increasing temperature.

Referring to the drawings, FIG. 1 shows a well 12 extending from thesurface of the earth 114 through overburden formation 16 into a shaleoil deposit 18. An underlying formation 20 is also indicated. The well12 may be suitably lined and equipped with tubing, etc in a conventionalmanner. A conduit 22 communicates at one end thereof to the top of thewell 12. The other end of conduit 22 may be connected to a source ofinjection fluid such as water saturated with H 8 and CO or may beconnected to means for recovering kerogen or bitumen from the shaledeposit 18. Means (not shown) are also provided for closing off theconduit 22 completely to shut in the well 12.

As an example of recovery of hydrocarbon values from oil shale inaccordance with a preferred embodiment of the invention, water having abrine content less than 50 ppm is introduced through the conduit 22 intothe well 12. Half of this water is saturated with CO and half with H 8,thereby forming a mixture of H CO and H SH O. This acid mixture ispumped down well 12 to deposit 18 under 1000 pounds pressure until thepressure at the bottom of the well reaches 600 psi (200 psi aboveformation pressure). The well 12 is then shut in for a period of 1 monthduring which time the acid solution dissolves the inorganic matrix inthe deposit 18 and the pressure at the bottom of the well graduallydrops to 450 psi (50 psi above formation pressure), at which time theacid solution has penetrated the deposit to the extent indicated by thesphere 24 in FIG. 1. The well is then opened up again and injection ofacid solution under pressure resumes until the pressure again rises to500 psi at the bottom of the well. The well is again shut in untilpressure drops to 50 psi, at which time the acid solution has penetratedthe deposit to an extent indicated by a sphere 26. Following a thirdcycle of pressure injection, a total volume of the deposit enclosedwithin a sphere 28 has been effected by the acid solution and has beenmade sufficiently permeable for kerogen to be recovered through the well12 in the form of a colloidal suspension. To facilitate this withdrawalof kerogen, 1 percent of a commercial surfactant material (benzenesulfonic acid) is included within the acid solution injected through thewell 12 during the injection cycles described above. Total elapsed timeto dissolve the inorganic matrix and render the deposit permeable withinthe sphere 28 is about 6 months.

To recover maximum hydrocarbon values from a shale formation, it isgenerally desirable to use more than one well similar to the well 12 ofFIG. 1. This is illustrated in FIG. 2, which shows an oil shale deposit32 with a number of wells such as 34 and 38 completed within the shaledeposit. By injection of H CO and H SI-I O as described above, withperiodic shutting in of wells, hydrocarbon values may be recovered fromwide areas of the deposit. The spheres of affected areas of the depositin which this occurs are indicated generally in FIG. 2 by dashed circlessuch as 36 and 40. It will be noted that these spheres overlap so as torecover hydrocarbon values from the maximum possible volume of thedeposit and that none of the spheres reaches the boundary of thedeposit. By keeping the spheres from reaching the boundary of thedeposit and avoiding fracturing of the shale, it is possible to takeadvantage of the extremely low permeability of the natural shale depositto prevent any loss of hydrocarbon values before they can be producedfrom the deposit.

While the invention has been described above with respect to certainpreferred embodiments thereof, it willbe understood by those skilled inthe art that various changes and modifications may be made withoutdeparting from the spirit and scope of the invention.

I claim:

1. A process for recovering hydrocarbon values from a subterraneandeposit of oil shale which comprises the steps of a. introducing H 8 andCO in water under pressure into said deposit until the pressure in thedeposit at the point of introduction of H 5 and CO in water is betweenabout 200 and about 1000 psi above the formation pressure of thedeposit;

b. then shutting in the deposit until the pressure at the point ofintroduction drops to less than about 50 psi above the formationpressure of the deposit; and

c. then recovering hydrocarbon values from the deposit.

2. The process of claim 1 in which the H 8 and CO in water mixture isformed by injecting water into the shale deposit through wells andintroducing H 5 and CO into such water at an elevation within the shaledeposit.

3. The process of claim 1 in which steps a and b are repeated until thereactant mixture of H 8 and CO in water has penetrated the shale depositthroughout spheres having a radius of between about 5 0 and about 500feet from the points of injection of such acids-into the deposit, eachof said spheres being at least about 50 feet from the boundary of thedeposit.

4. The process of claim 2 in which the H SH O and H CO are formed,respectively, by saturating water with H 5 and CO 'and in which theresulting solution comprises between about 30 and about volume percentwater saturated with CO with the. remainder comprising water saturatedwith H 8. v

5. The process of claim 1 in which H 8 and CO in water are introducedinto the deposit by saturating water with CO and H 8 and then injectingsaid water into wells extending into the deposit.

6. The process of claim 1 in which hydrocarbon values are recovered fromthe shale deposit in the form of kerogen in colloidal suspension inwater.

7. The process of claim 6 in which surfactant is added to the H SH O andH CO to facilitate suspension of kerogen therein for withdrawal ofkerogen from the deposit.

1. A PROCESS FOR RECOVERING HYDROCARBON VALUES FROM A SUBTERRANEANDEPOSIT OF OIL SHALE WHICH COMPRISES THE STEPS OF A. INTRIDUCING H2S ANDCO2 IN WATER UNDER PRESSURE INTO SAID DEPOSIT UNTIL THE PRESSURE IN THEDEPOSIT AT THE POINT OF INTRODUCTION OF H2S AND CO2 IN WATER IS BETWEENABOUT 200 AND ABOUT 1000 PSI ABOVE THE FORMATION PRESSURE OF THEDEPOSIT, B. THEN SHUTTING IN THE DEPOSIT UNTIL THE PRESSURE AT TH POINTOF INTRODUCTION DROPS TO LESS THAN ABOUT 50 PSI ABOVE THE FORMATIONPRESSURE OF THE DEPOSIT, AND C. THEN RECOVERING HYDROCARBON VALUES FROMTHE DEPOSIT.
 2. The Process of claim 1 in which the H2S and CO2 in watermixture is formed by injecting water into the shale deposit throughwells and introducing H2S and CO2 into such water at an elevation withinthe shale deposit.
 3. The process of claim 1 in which steps a and b arerepeated until the reactant mixture of H2S and CO2 in water haspenetrated the shale deposit throughout spheres having a radius ofbetween about 50 and about 500 feet from the points of injection of suchacids into the deposit, each of said spheres being at least about 50feet from the boundary of the deposit.
 4. The process of claim 2 inwhich the H2S-H2O and H2CO3 are formed, respectively, by saturatingwater with H2S and CO2 and in which the resulting solution comprisesbetween about 30 and about 70 volume percent water saturated with CO2,with the remainder comprising water saturated with H2S.
 5. The processof claim 1 in which H2S and CO2 in water are introduced into the depositby saturating water with CO2 and H2S and then injecting said water intowells extending into the deposit.
 6. The process of claim 1 in whichhydrocarbon values are recovered from the shale deposit in the form ofkerogen in colloidal suspension in water.
 7. The process of claim 6 inwhich surfactant is added to the H2S-H2O and H2CO3 to facilitatesuspension of kerogen therein for withdrawal of kerogen from thedeposit.